1. Field of the Invention
This invention relates generally to materials separator apparatus and is concerned more particularly with a materials separator having eddy-current inducing means for separating electrically conductive items from commingled dielectric items of nonferromagnetic materials.
2. Discussion of the Prior Art
In the recycle processing of waste materials, solid municipal waste initially may be shredded into items of more manageable size which are directed into a stream, as by feeding them onto a moving endless conveyor belt, for example. The stream of shredded waste material may be conducted to a conventional air classifier for removing light fraction items, such as paper products, for example. A resulting stream of heavy fraction items then may be passed through a conventional magnetic separator where ferromagnetic items of high permeability material, such as iron products, for example, are removed from the stream. The non-ferromagnetic materials then remaining in the stream comprise dielectric items, such as plastic, rubber, wood and glass, for example, and electrically conductive items such as aluminum, silver, copper and zinc, for example. These electrically conductive items constitute a significant percentage of the total resale value of recycled municipal waste material. Consequently, there has been developed in the prior art a number of materials separators for segregating electrically conductive items from commingled dielectric items of nonferromagnetic materials.
In U.S. Pat. No. 4,003,830 granted to E. Schloemann on Jan. 19, 1977 and assigned to the present assignee, there is shown a ramp type of nonferromagnetic materials separator having a longitudinally sloped surface which extends transversely at substantially right angles to an imaginary plane passed vertically through its longitudinal centerline. This ramp type of separator is provided with steady-state magnetic means for establishing along said sloped surface a spatially alternating series of oppositely polarized and substantially parallel magnetic stripes which extend transversely at an oblique angle with respect to the longitudinal centerline of said sloped surface. A stream of commingled nonferromagnetic items is directed onto the upper end portion of said sloped surface and adjacent a first longitudinal side thereof to slide down the sloped surface under the influence of gravity.
Since the dielectric items of nonferromagnetic material in the stream are unaffected by the array of oppositely directed magnetic fields established by said magnetic stripes, they continue to slide down the longitudinally sloped surface of the separator and may be collected at the bottom adjacent said first longitudinal side thereof. On the other hand, the electrically conductive items of nonferromagnetic material in passing sequentially through the oppositely directed magnetic fields of the array have induced in them eddy-currents which coact with the magnetic fields. As a result, these electrically conductive items have exerted on them a resultant force which is directed upwardly of the longitudinally sloped surface and substantially perpendicular to the magnetic stripes. Consequently the resultant forces have respective components which deflect the electrically conductive items laterally while they are sliding longitudinally down the sloped surface. Thus, the electrically conductive items may be collected at the bottom of the sloped surface and adjacent the second or opposing longitudinal side thereof.
Although the described separator operates satisfactorily for segregating electrically conductive items from commingled dielectric items of nonferromagnetic materials, its efficiency in the segregation process is not one hundred percent. Consequently, there may be disposed between the respective containers for collecting the dielectric items and the electrically conductive items at the bottom of the ramp one or more containers for collecting the "middlings". The "middlings" comprise a mixture of the dielectric and the electrically conductive items resulting from incomplete separations of these items. In some instances, the percentage of dielectric items in the "middlings" may be considered to be objectionable because, among other reasons, excessive lateral spreading of the dielectric items takes place as they slide longitudinally down the ramp and high feed rates cause a relatively larger number of collisions to occur on the ramp surface between the dielectric items and the deflected electrically conductive items.